Underground Construction - July 2019 - 37

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Polyester, vinyl ester and epoxy resins make up the
majority of thermoset resins used in the CIPP process.
Polyester resins and vinyl ester resins are similar in
chemistry. Epoxy resins use a different chemistry. All
of the mentioned resins exhibit similar mechanical
properties, corrosion resistance in the municipal market
and anticipated service life when used properly.
Polyester resins are manufactured by a chemical
method called "aldol condensation". The components
of this reaction are acids and polyols reacted together
by various catalyst systems. When a resin supplier
talks about "isophthalic" or "terephthalic" resins, the
supplier is telling us the acid component in the resin. In
some cases, the supplier may call a resin an NPG/Iso
or NPG/Ortho resin. In that case the supplier is telling
us both the polyol and acid components of the polymer.
This initial reaction is not the final step in creating the
final product used in the CIPP process. This "adduct"
is generally a crystalline solid which would be difficult
for use in molding applications and is now ready to be
blended with a reactive diluent. The diluent will make
the resin into a liquid system at room temperature,
will take part in the reaction, and crosslink providing
improved mechanical properties. Styrene is the most
commonly used reactive diluent in creating these
polymers. It is the least expensive, the most reactive
and safe when used properly. There are also nonstyrene reactive diluents available, some are non-volatile
organic compounds (non-VOCs). There are numerous
combinations of these components available from
resin suppliers.
The choice of which resin to select for the CIPP process
boils down to the process requirements and the final
properties desired.
For processing in the CIPP process, the resin used
must be of the proper liquid consistency. It must wet
the tube material properly, without air voids, quickly,
and not drain from the tube when processed. The
resin must also be stable enough to remain a liquid
throughout the wet out, transport to the jobsite and
installation process. The resin must also use an initiator
system with little risk of problems. Historically solid
initiators in heat cured CIPP processing have presented
problems with poor mixing. Other heat cured initiators
have proven unable to provide the proper pot life for
the process. Newer initiator offerings in the heat cured
resin sector are proving to minimize the risk of these
problems. Ultraviolet (UV) cured resin/tube systems
tend to be available directly from the tube manufacturer,
eliminating the need for a contractor to be involved

in that part of the process. These UV cured systems
come with significantly longer pot lives when properly
stored. Processing is slightly different and UV cured
systems offer speedy cures for the applicable liner
sizes. Limitations in liner diameter and thickness must
be considered when considering this process.
The final properties of the cured liner are generally
stipulated in the contract documents from the owner.
These properties generally also include mechanical
property requirements, corrosion resistant requirements
and anticipated service life requirements. For almost
all of the commercially available resins from
manufacturers of CIPP resins, resin formulations are
designed to meet these needs. Contractor installation
requirements such as liner thickness, free of air voids,
finning and blistering are generally not dependent on
resin specific properties.
While the above describes polyester and vinyl ester
resins, epoxy resins differ in chemistry. Epoxies are
100% solids, unlike most polyester and vinyl ester
resins which contain a reactive diluent. Epoxies are
two-part systems comprised of an epoxide and a
hardener. Depending on the formulation, epoxy system
ratios of epoxide and hardeners differ. Some formulas
are 1:2, some 2:1, etc. Generally, epoxy systems and
vinyl ester resin systems have similar mechanical,
corrosion resistant and expected service life properties.
Pot lives vary with epoxy systems but generally are
shorter than polyester and vinyl ester resin systems.
With the emphasis being placed on renovating drinking
water systems using the CIPP method, much work
has been placed on resin manufacturers to develop
resin systems that are user friendly and that will pass
ANSI 61 requirements to be drinking water certified.
Epoxy resins are currently used in drinking water and
other pressure applications. Vinyl ester resins with
newer reactive diluents are also being used in UV cured
systems and will soon be used in heat cured systems.
Over the past 40 plus years, resin formulations have
evolved to work better in the CIPP process. With
new initiators, sustainable raw materials, non-VOC
additives and other improvements, working with the
CIPP process has become easier and more reliable.
Pressure pipes are being renovated successfully.
Drinking water lines are being renovated. Concerns
about environmental contamination are being reduced.
And resin producers won't stop there. There will be
more and better developments in raw materials and
processing for the CIPP industry in the future.


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Underground Construction - July 2019

Table of Contents for the Digital Edition of Underground Construction - July 2019

Contents
Underground Construction - July 2019 - FC
Underground Construction - July 2019 - IFC
Underground Construction - July 2019 - Contents
Underground Construction - July 2019 - 4
Underground Construction - July 2019 - 5
Underground Construction - July 2019 - 6
Underground Construction - July 2019 - 7
Underground Construction - July 2019 - 8
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Underground Construction - July 2019 - IBC
Underground Construction - July 2019 - BC
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